Second step to Validating Open Graph: OG namespace

Your second step to getting Open Graph to validate is to get the OG namespace in scope. The OG namespace is what you see prefixed to the value of each of the property attributes of each of the Open Graph meta elements, such as: 'og:title', 'og:image', and so on.

You import the Open Graph schema and create the OG namespace using the HTML5 native attribute named 'prefix'. The import instruction of the Open Graph schema can be added to the HTML element named 'HTML' or to the element 'HEAD'.